1. Field of the Invention
The present invention relates to permanent magnet rotating electric machines.
2. Description of the Related Art
It is known that the efficiency of rotating electric machines can be increased by using permanent magnets to generate a field magnetic flux. Recently, the magnetic flux density in an air gap has been increased by using magnets with enhanced properties, so that it is possible to configure an efficient and compact rotating electric machine. Moreover, with enhancement of the properties of magnets and advancement of technologies, the range of the use of permanent magnet rotating electric machines has been increased, and permanent magnets with enhanced properties have become used even in rotating electric machines for high-speed rotation and large-sized rotating electric machines.
Magnets with enhanced properties have high electrical conductivity, and it has been a problem in that in high-speed or large-sized rotating electric machines, a decrease in efficiency is caused by an eddy current generated in magnets. In order to solve this problem, Japanese patent application Unexamined publication No. H11-4555A/1999 describes a rotating electric machine in which an eddy current in a permanent magnet is decreased by interposing insulating materials between electrically conductive permanent magnet materials having enhanced properties.
However, with the technique described in the above prior art, the difference in the coefficient of thermal expansion between an insulator and an electrically conductive permanent magnet causes stress, which sometimes results in, for example, breakage of the magnet. Moreover, since insulating members are interposed between magnet pieces, it takes time and cost for uniformly disposing the insulating members and for manufacturing the rotating electric machine. Furthermore, due to the disposition of insulating members between magnet pieces, the above-mentioned technique brings problems such as a reduction in the properties of magnets.